The present invention relates to a presensitized plate for use in making a lithographic printing plate requiring no dampening water (hereinafter referred to as "dry PS plate") and in particular to a dry PS plate which is excellent in adhesion between the substrate and the light-sensitive layer in wet state during developing treatment and which can provide a lithographic printing plate requiring no dampening water (hereunder referred to as "dry lithographic plate") improved in the printing durability and resistance to scratch.
There have been proposed a variety of dry PS plate in which a silicone rubber layer serves as non-image portions (see, for instance, Japanese Patent Publication for Opposition Purpose (hereunder referred to as "J. P. KOKOKU") Nos. Sho 44-23042 (U.S. Pat. No. 3,677,178), Sho 46-16044 (U.S. Pat. No. 3,511,178), Sho 54-26923 (U. S. Pat. No. 3,894,873), Sho 61-54222 (U.S. Pat. No. 4,342,820) and Sho 63 26247).
There have been known two types of methods for making printing plates from dry PS plates of this kind, one of which comprises dissolving a light-sensitive layer on the image areas with a developer to remove a silicone rubber layer present thereon to thus give images (J. P. KOKOKU No. Sho 46-16044 (U.S. Pat. No. 3,511,178)) and the other of which uses a dry PS plate comprising a photoadhesive light-sensitive layer or a photopeelable light-sensitive layer and a silicone rubber layer, comprises selectively removing only the silicone rubber layer on the image areas (see J. P. KOKOKU No. Sho 54-26923 and Japanese Patent Unexamined Publication (hereunder referred to as "J. P. KOKAI") No. Sho 56-80046 (U.S. Pat. No. 4,342,820)).
The latter case will be explained below using a dry PS plate comprising a photoadhesive light-sensitive layer and a silicone rubber layer by way of example. The photoadhesive light-sensitive layer and the silicone rubber layer of this PS plate are strongly adhered to one another through exposure to light. Therefore, the development of the PS plate is performed using a developer which does not substantially dissolve the photoadhesive light-sensitive layer and is capable of swelling the light-sensitive layer and/or the silicone rubber layer. Thus, the silicone rubber layer on the image areas is selectively removed and peeled off to expose the light-sensitive layer which serves as an ink receiving part. However, this plate making method suffers from the following problems. For instance, since the adhesion between the light-sensitive layer and the silicone rubber layer is insufficient, a part of the light-sensitive layer on the nonexposed portion is peeled off, as a result the surface of the substrate is exposed. The ink receptivity of the light-sensitive layer is different from that of the exposed substrate. This difference is possibly reflected on the printed matters and thus satisfactory copies cannot be obtained at all.
Under such circumstances, many attempts have been directed to the improvement in the adhesion between the light-sensitive layer and the silicone rubber layer. For instance, J. P. KOKOKU No. Sho 61-54219 discloses a method in which a primer layer containing an epoxy resing positioned between these layers. This primer layer can ensure good adhesion to the substrate, but the adhesion thereof to the light-sensitive layer is greatly affected by components of the latter. More specifically, if the components of the light sensitive layer are changed in order to improve, for instance, the printing durability and resistance to scratch of the resulting lithographic plate as well as the sensitivity and fine image-reproduction Of the PS plate, the adhesion between the primer layer and the light sensitive layer is impaired.
Moreover, the resistance to scratch of the PS plate is greatly dependent upon the flexibility of the light-sensitive layer as well as that of the primer layer. In this respect, there has long been desired for the development of a primer layer having flexibility higher than that of the epoxy resins. As an attempt for improving the flexibility of the primer layer, there has been known a method in which a rubber component is used for forming a primer layer and the rubber component is a polyurethane (see J. P. KOKAI No. Sho 61 163343 which relates to a dry PS plate comprising a photopeelable light sensitive layer). However, this method is still insufficient in the adhesion of the primer layer to the substrate.